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289 Potential Vacuum issue

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    289 Potential Vacuum issue

    Hi all,

    Long time member but first time poster! 18 months ago I purchased my first classic car from Chris on here (yanktankmad) and all has been well but I wondered if anyone could help with identifying an issue when I connected a vacuum gauge to my intake manifold.

    The reading seems to be very unstable which worries me but Iím not sure what the issue could be or if I need not worry. I took a video to help illustrate:

    Any advice you can give would be great!


    do you have a high lift cam?this might cause it


      This is a useful run through on vacuum reading and stability.


        Thank you for your help!

        Mark - Iím not sure if I have a high lift cam, is there an easy way for me to tell?

        Thanks Rider - I had seen that video which suggests it is worn valve guides but I didnít know if anyone on here would have another opinion!



          That vacuum reading that you have is perfectly normal. There is a bit of pulsing and some slower oscillation from the engine. Also you engine sounds fine idling nice and smooth. If you get a hose clamp from say a tropical fish shop and squash the gauge tube a bit with it you will find the rapid needle oscillations smooth out. Any issues with valves or a bad cylinder or a vacuum leak can (but not in all cases) show themselves as a slow oscillation of the gauge over a greater range, coupled with a not so smooth idle. When you get the reading smooth you can try adjusting the mixture screws to get the highest reading possible and see if you can smooth out the slower oscillation, but as said your engine sounds fine.
          Last edited by ALLAN R; 28-10-2019, 03:19 PM.